There are many situations where it is desirable to provide guidance for an aircraft into and out of an unprepared area without an established airfield. For example, it would be desirable to insert assault troops to and from a remote battlefield. Another example would be emergency medical services operations used to evacuate and transport severe trauma accident victims or other individuals in need of medical attention by air to the nearest hospital. In all cases, there is a need to safely guide an aircraft such as a helicopter to an appropriate landing zone where there is no established airfield. In this regard, a detailed and comprehensive understanding of the relevant conditions in a potential landing zone is crucial to safely landing the aircraft and subsequently taking off.
In non-military situations, only visual acquisition of the landing area by the crew of the aircraft in good visual meteorological conditions is possible. In secure military situations, the on-the-ground armed forces may employ a glide angle indicator light (GAIL) apparatus to assist in guiding an aircraft to a safe landing in a confined area. There are significant limitations to these approaches, however. Visual terminal guidance is not possible in poor weather (very low visibility) conditions. GAIL systems are limited to night time operations in good weather conditions and they are difficult to install.